一段代码没看懂，请教指点

sqlCon = new SqlConnection(connString);
            if (sqlCon.State == ConnectionState.Closed)
            {
                sqlCon.Open();
            }
            SqlCommand sqlCmd = new SqlCommand();
            sqlCmd.Connection = sqlCon;
            sqlCmd.CommandText = "Select * from tb_admin Where username='" + txtName.Text.Trim() + "'";
            sqlDa = sqlCmd.ExecuteReader();
            if (Session["UserName"] == null || Session["UserName"].ToString() == "")
            {
                if (sqlDa.HasRows)
                {
                    while (sqlDa.Read())